Photographic material of emulsions of different gamma and sensitivity

ABSTRACT

Photographic copy of image that is partly continuous tone and partly line is made with a single exposure of entire image on combination of two silver halide emulsions carried by a supporting surface that reflects at least half the light reaching it, one emulsion having a gamma between 0.8 and 1.2 and a maximum density of at least 1.4, the other being slower than the first by at least 6* DIN, having a gamma between 2.0 and 4.0 and at least 1.0 greater than the first and having a maximum density about the same as the first. The emulsions can have their respective maximum sensitivities in different portions of the spectrum and can contain dyes that absorb in such spectrum portion to adjust respective sensitivities.

United States Patent Lohmer et al. Dec. 4, 1973 [54] PHOTOGRAPHICMATERIAL 0F 3,411,908 11/1968 Crawford 96/87 g gg il gis DIFFERENT GAMMAAND FOREIGN PATENTS OR APPLICATIONS 604,761 9/1960 Canada 96/68 [75]Inventors: Karl Lohmer; Werner Verburg, both of Leverkusen, Germany [63]Continuation of Ser. No. 688,354, Dec. 6, i967,

abandoned.

[30] Foreign Application Priority Data Dec. 14, 1966 Germany A 54364[52] US. Cl 96/68, 96/44, 96/45 [51] G03c l/76, G03f 5/00 [58] Field ofSearch 96/68 [56] References Cited UNITED STATES PATENTS 7/1964 Hellmig96/68 Primary Examiner-Norman G. Torchin Assistant ExaminerAlfonso T.Suro Pico Att0rneyConnolly & l-lutz [57] ABSTRACT Photographic copy ofimage that is partly continuous tone and partly line is made with asingle exposure of entire image on combination of two silver halideemulsions carried by a supporting surface that reflects at least halfthe light reaching it, one emulsion having a gamma between 0.8 and 1.2and a maximum density of at least 1.4, the other being slower than thefirst by at least 6 DIN, having a gamma between 2.0 and 4.0 and at least1.0 greater than the first and having a maximum density about the sameas the first. The emulsions can have their respective maximumsensitivities in different portions of the spectrum and can contain dyesthat absorb in such spectrum portion to adjust respective sensitivities.

3 Claims, No Drawings PHOTOGRAPHIC MATERIAL OF EMULSIONS OF DIFFERENTGAMMA ANlD SENSITIVITY This application is a continuation of Ser. No.688,354 filed on Dec. 6, 1967, now abandoned.

This invention relates to a photographic material for use in theproduction of reflection copies for the photomechanical production ofprinting forms.

In the photomechanical production of printing forms, one generallystarts with an original which has been obtained photographically. Thedensity values of this original are converted into electrical values bypoint-bypoint scanning with a measuring beam. These measured values areused in a mechanical apparatus which operates synchronously with thescanning device to produce a printing form by mechanical means.

In the production of cylindrical printing forms, the original may bearrangedcylindrically in order to facilitate synchronization between thescanning device and the cylindrical printing form, so that in thesimplest case, where the conversion scale is 1:1, very simplegeometrical relationships are obtained.

The photographic original used for the photomechanical production ofprinting form must meet high requirements. This material must renderboth continuous-tone and line images of optimum quality and in additionit should have good dimensional stability. This requirement of yieldingoptimum reproduction both of continuous-tone and of line images wouldappear to be a contradiction in terms in that a relatively low contrastis required for a continuous-tone image whereas a steep gradation isrequired for optimum reproduction of a line image.

These contradictory requirements can be met if a photographic materialis produced in such a way that either a high or low gamma value results,depending on the choice of copying light. This is achieved, for example,either by mixing an orthochromatic (green sensitive) line emulsion witha blue-sensitive continuoustone emulsion or applying one such emulsionover the other. If this material is exposed through a blue filter, onlythe silver halide emulsion which yields a low gamma will bephotographically active provided the threshold sensitivity of thegreen-sensitive silver halide emulsion is sufficiently high comparedwith the bluesensitive emulsion.

The use of such a material, however, requires considerable waste of timebecause the line image in a combined original which contains partlycontinuous-tone and partly line images must be covered by a black maskwhile the continuous image is exposed behind a blue filter, andconversely the continuous-tone image must be covered with a mask duringexposure of the line image behind a yellow filter.

The object of the present invention is to provide a photographicmaterial by means of whichboth continuous-tone and line image of goodquality can be. reproduced by a single exposure.

We now have found that a photographic material which contains at leasttwo silver halide emulsions differing from each other in gamma andsensitivity, which emulsions may be either mixed in one layer orarranged separately in two layers, may be used for this purpose. A dyewhich absorbs light from that range of wavelengths to which the lowcontrast silver halide emulsion is sensitive is added at least to thatemulsion which is responsible for reproduction of the continuous-tones.

The density of the dye in this region is preferably about 0.8 to 1.2.

The light-sensitive silver halide emulsion layer or layers of thephotographic material according to the invention are applied direct to adimensionally stable support which reflects diffusely from its surfaceessentially all light, but at least 50 percent. In order to achievesufficient sharpness, the light must not penetrate to any significantextent into the support but must be reflected on the surface.Surprisingly with this material one obtains such good reproduction ofdetail that copied line images suffer no detectable loss in sharpnesseven if they are copied on a photographic material having a gammasuitable for continuous-tone images.

A suitable support is, for example, a polyester film especially,polyethylene terephtylene', containing white pigments. Alternatively,paper the surface of which has been rendered water-resistant byapplication of layers of synthetic resin containing white pigment, maybe 'used. The dimensional stability of the paper'may be improved bybacking it with metal foils. Thus, good results were obtained with paperwhich had been rendered dimensionally stable by backing with analuminium foil and which had been made waterproof by coating the surfacewith polyolefine, preferably polyethylene, layers containing TiO Thewhite pigment content inthe layer immediately below the light-sensitivesilver halide emulsion layer is necessary if one is to achieve therequired sharpness.

The light-sensitive silver halide emulsions are prepared in the usualmanner. The emulsions with flatter gamma for reproduction ofcontinuous-tone images generally contain silver bromide, optionally witha small addition of silver chloride and a minor quantity of silveriodide. The emulsions with steeper gamma, which are higher in contrast,generally contain mixtures of silver chloride and silver bromide. Theusual hydrophilic film-forming binding agents such as polyvinyl alcohol,alginic acid derivatives or preferably gelatin, may be used as bindingagents for the silver halide emulsion layers.

The usual photographically inactive dyes are applied as masking dyes.Suitable products are described in the literature.

The thickness of the silver halide emulsion layer where only one is usedis about 3 to 10 u, preferably about 5 p..

The emulsion with the flatter gamma is preferablyonly blue-sensitivewhereas the emulsion with the steeper gamma and higher contrast may inaddition he green-sensitive and/or red-sensitive. The emulsion with theflatter gamma, which records the continuous tones, should be so composedas regards its silver concentration and other photographic propertiesthat it has a maximum density of at least 1.4 under the usual conditionsof development.

The low contrast silver halide emulsion has a gamma between 0.8 and 1.2,the high contrast silver halide emulsion a gamma of 2.0 and 4.0. Thedifference in gamma between the two emulsions should be at least 1.0.

The sensitivity to white light of the high contrast silver halideemulsions is at least 6 DIN less than that of the low contrast emulsion.This amounts to a difference of two or more shutter stops.

Example 1 A silver iodobromide gelatin emulsion containing 5 mol% ofsilver iodide based on the total silver halide, and which has not beenoptically sensitized, contains a yellow masking dye (as described inUllmann, Encyklopadie der Techn. Chemie, Vol. 13, page 627, 3rd edition)and reproduces continuous tones with gamma of one, is applied to abiaxially prestretched support of polyethylene terephthalate that hasbeen rendered opaque by incorporation of titanium dioxide. The emulsionis applied in such the way that a maximum density of developable silveris .4. The concentration of the masking dye is so calculated that ayellow density of about D 1.0 is obtained in the unprocessed material.

A high contrast silver chlorobromide gelatin emulsion (containing 70mol% of silver chloride based on the total silver halide) which has notbeen optically sensitized and which has a 'y 4, the sensitivity to whitelight of which is only one-twentieth of the sensitivity of the firstemulsion, is applied onto this first emulsion layer in such a way thatthe second emulsion has the same silver content per square meter. Theabove masking dye may also be added to this second layer to correct thesensitivity.

A material is thereby obtained which on exposure behind a grey testwedge and the usual photographic processing including development andfixing in the following baths:

Developer: 1 g. p-methylamino phenol 3 g. hydroquinone 13 g. of sodiumcarbonate g. of sodium sulfite sicc.

1 g. potassium bromide 1000 ml. of water Fixingbath:

200 g. of sodium thiosulfate cryst.

50 g. potassium metabisulfite 1000 ml. of water has a higher gamma inthe density region above 1.5 than in the density region below 1.5. Anoriginal which is composed of continuoustone and line transparenciessuitable for photogravure is copied onto the resulting material so thatthe lightest density value to be reproduced in the subsequent print isreproduced as grey tone of density 1.6. The resulting copy is bestsuited for the photomechanical production of printing forms. Thisprocess is suitable in particular for use in the production of printingforms by the so-called heliograph block method (Hell, Kiel).

Example 2 The two emulsions used in Example 1 are so chosen that for agiven concentration of masking dye, they have a sensitivity ratio of1:20. The two emulsions, which have the same silver content, are nowmixed in a ratio of 1:1 and the mixture is applied to the supportdescribed in Example 1 so that the same amount of silver is present perunit surface area as in the photographic two-layered material used inExample 1. Processing is otherwise carried out as described in Examplel. A copy is obtained which is excellently suitable for the productionof printing forms.

Example 3 The following emulsion mixture is applied onto the supportdescribed in Example 1. One emulsion is a continuous-tone silverchlorobromide emulsion containing 30 mol% of silver bromide bored on thetotal silver halide and sensitized to blue light. To this emulsion isadded a high contrast silver chlorobromide emulsion containing 96 mol%silver chloride and sensitized to green light, the additive being in theratio of 1:1. The yellow masking dye of Example 1 employed in the samemanner.

It is now no longer important to observe accurately the sensitivityrelationship between the two silver halide emulsions since thecharacteristic curve of the high contrast emulsion component can beshifted in relation to the characteristic curve of the low contrastemulsion component by suitable choice of the color of the copying light.A higher gamma in the density region of above 1.5 than that inthe'density-range of below 1.5 can therefore easily be achieved.

Further processing is carried out as in Example 1, except that the colorof the copying light is adjusted accordingly.

Example 4 In a manner analogous to Example 3, the emulsion mixture isapplied onto paper which is coated on both sides with a polypropylenelayer. TiO pigment is incorporated into that polypropylene layer ontowhich the silver halide emulsion layer is arranged,-so that light isreflected from the surface of the pigmented polyolefine layer. Theprocedure is otherwise analogous to that used in Example 3.

Example 5 In a manner analogous to Example 3, the emulsion mixture isapplied onto a paper support provided with polyethylene layers asdescribed in Example 4. This support is backed on the rear side with athin aluminium foil to increase the dimensional stability. The procedureis otherwise as indicated in Example 3.

What is claimed is:

1. In the preparation of a reproduction of an image that is partlycontinuous tone and partly line the steps of preparing a light sensitivelow contrast silver halide emulsion which yields a gamma suitable to acontinuous tone reproduction and a high contrast silver halide emulsionwhich yields a gamma of at least 1.0 greater than the low contrastemulsion and the high contrast emulsion being applied to a dimensionallystable support which reflects light from its surface, exposing thephotographic material to light and subjecting the exposed material tophotographic processing including development and fixing in suitablebaths and copying continuous-tone and line images, the improvementaccording to which absent masking of the line image part or thecontinuous image part a single undelineated exposure is used to exposeto that image ,a light-sensitive photographic silver halide combinationhaving the support white pigmented to provide a surface that diffuselyreflects at least half the light reaching it, and the two silver halideemulsions coated and dried on completely cover a common area of thesurface, one of the emulsions having a gamma between 0.8 and 1.2 and amaximum density of at least 1.4, the other emulsion having a speed indexvalue at least 6.0 DlN slower than the first, having a gamma between 2.0and 4.0 and at least 1.0 greater than the first, and having a maximumoptical density substantially the same as the first emulsion,

3,776,733 6 contained in the first emulsion having the ability to abentvisible wavelengths. sorb light to which that emulsion responds, thedensity of the dye being between 0.8 and 1.2, and developing emulsion isonly blue sensitive, the other emulsion 1s and fixing the thus-exposedcombination.

2. The invention of claim 1 in which the two emul- 5 sensitized togreen' sions have their respective sensitivity maxima at differ- 3. Theinvention of claim 1 in which the low contrast

2. The invention of claim 1 in which the two emulsions have theirrespective sensitivity maxima at different visible wavelengths.
 3. Theinvention of claim 1 in which the low contrast emulsion is only bluesensitive, the other emulsion is sensitized to green.